Case-hardening process



July 1 11924n F. A. BOND CASE HARDENING PROCESS Filed July la' 1921 z sheets-sneu 2 Patented July l, 1924.

l UNITED s'm'ras PATENT OFFICE,`

FRANK A. BOND, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOB TO 'UNITED STATES CHAIN & FORGING COMPANY, A CORPORATION 0F DEIIIAWARE.v

casa-Hamam@ rnocnss.

Application mea July 1s, 1921. serial no. 485,6911.

To all lwhom t may concern:

Be i known that I, FRANK A. BOND, a citizen of the United States, and resident of Pittsburgh, in the county of Allegheny and 5 State of Pennsylvania, have invented a new.

and useful Im rovement in Case-Hardening Processes; an I do hereby declare the following to be a full, clear, and exact description thereof.

My invention relates to the hardening of metal to produce a hard and uniform surface layer of superior wear-resisting qualities, a tough, strong and unhardened core, and an intermediate layer of gradually varying hardness interposed between the hard outer layer Vand the soft, tough core.

A further object of my invention is to provide a process of producing case-hardened articles of the above indicated character, by which the depth to which the hardening effect penetrates may be closely controlled, and which shall produce uniformly hardened articles having uniform internal structure. My process consists, in general, in providing a fused bath' of case-hardening material containing a substantial portion of a cyanide, preparing the articles to be treated by preheatingthem at least to their upper point I of decalescence and preferably to approximately the samedtemperature as the temperature of the fusedbath, then introducing the preheated'articlesl into the fused bath and keeping them there for a period of time which depends on the nature of the articles and theresults to be produced. The temperature of the bath and of the preheated articles also depends lupon the exact results to be produced, and may be varied within 3@ considerable-limits, as will more fully appear below;

v I am aware that potassium cyanide,

sodium cyanide, and other cyanide materials have long been used for case-hardening. Usually the cyanide material is appliedto the articles to be case-hardened by sprinkling the dry cyanide upon the articles, and then heating the articles to melt the cyanide. Other methods heretofore used involve melting the cyanide to form a fused bath, and introducing the articles to be case-hardened into the bath, but so far as I am aware it has never been proposed to prepare the articles before definite finalV temperature.

hardening by heating the articles to a temperature approximately that of the fused bath, nor'has it ever been proposed to continue the treatment -of the preheated articles in the fused bath for such a period of time as I have found to be necessary for the proper working of my process.

My present process was devised in connection with the hardening of anti-skid chains for automobiles and motor trucks. These chains must have the highest possible wearresisting qualities, and I have found that y the process described herein imparts to such chains a hardness and resistance to wear which is not possible in any other case-hardening methods heretofore used.

It will be understood that, although my process is of value as applied to the hardening of wheel chains, it is by no means limited to this use, but may be employed with equally good results for hardening a large number of other metal articles where hardness and resistance to wear are important, such as machine parts, driving chains for coal mining machines, and many other articles.

In the accompanying drawings, which show by way of example one form of apparatus suitable for carrying out my process, 'y Fig. 1 is a vertical central sectional view through the apparatus for treating the articles with the fused bath, the preh'eating furnace being indicated diagrammatically; Fig. 2 is an enlarged vertical sectional view of a portion of the apparatus of Fig. 1, the section being taken substantially on the line 2 2, Fig. 3;-and Fig. 3 is a somewhat diagrammatic plan view of the apparatus shown in Fig. 1.

Referring to the drawings the num ral 2 designates a preheating furnace which may be of any desired construction and which is therefore not illustrated in detail. This furnace is preferably of the type in which the articles to be heated are introduced at one end and are movedl gradually through the furnace, being thereby heated to a, M0

If relatively small articles are to be treated, such as crosschains for use on vehicle wheels, they are preferably sent through/the furnace in metal pans or other suitable containers:

At the, discharge end ofthe furnace 2 is a suitable transfer 'mechanism for conveying the preheated articles from the furnace t the case-hardening baths. As shown, this transfer mechanism comprises a set of arms 3 mounted uppn a horizontal sha-ft 4 which may be rocked to allow the articles to slide into the case-hardening pots. An apron 5 or the like may be provided, as shown in Fig. 1, to guide the articles from the furnace to the treating pots which are arranged circularly on a frame consisting of radial arms 11, and a circular horizontal plate 12 suspended from the arms 11. The radial arms 11 are all secured to a circular central casting 13 which is carried by a vertical central shaft 14 mounted in bearings 15.and 16 on a supporting frame 17. A bevel' gear wheel 18 is secured to the vertical shaft 14 at its lower end and meshes with abevel pinion 19 secured to one end of a horizontal counter-shaft 20 which also carries a spur gear 21 meshing with a driving pinion 22 'on a shaft 23 which is connected through a set of reducing gears indicated diagrammatically at 25 to the armature shaft 26 of an electric motor 27. rll`he power connections just described serve to rotate the vertical shaft 14, and with it the circular frame carrying the case-hardening pots 10. rllhis rotation may be intermittent, the motor 27 being started and stopped to give the frame a partial rotation atsuitable intervals, or the rotor may run continuously an rotate the frame at a slow speed, sufficient to present the treating pots 10%,L to thefurnaee ,can also be produced by means of various power connections, and it will therefore be understood that these particular arrangements of shafts and gearing are shown herein by way of example only.

The circular plate 12 is provided with radial flanges 28 for attachment to the under side of the radial arms 11,-and with other flanges 29 forming rectangular seats for the pots 10. The plate 12 is suspended directly above a circular furnace 30, composed of 'brickwork or the like, and having an annular heating channel 31 into which the pots 10 extend. The pot-s 10 are supported from the circular plate 12 by means of flanges 32. Annular flanges 33 are formed on the underside of t-he circular plate 12 and extend into annular grooves 34 formed in the top of the furnace 30, the grooves 34 being filled with granular heat-insulating material 35. 'llhe plate 12 forms a cover for the furnace 30, and the flanges 33, being vembedded in the granular material 35, substantially prevent the escape of heat around the upper edges of the furnace.

The furnace 30 is heated by means of any convenient number of burners which may be arranged, for example, as shown in Fig. 2, each burner consisting of a pipe 40 for ad Monaci mitting gas or fuel oil supplied from the pipe 41. rll`he pipe 40 extends into an air inlet opening 42 of larger diameter. than the pipe 40, and the. combustion mixture passes into the channel 31 through an opening 43.

1n operation, a quantity of fused cyanidecontaining material, suiiicient to cover the articles to be treated, is placed in each of the pots 10. 'llhe temperature of the fused bath is maintained constant by suitable regulation of the burners 40, and this temperature may vary from 12000 F. to 1750o or 1800O F. rlhe composition of the bath may be varied considerably, so long as it contains a substantial proportion of cyanide material. @ne composition which ll have found suitable for this purpose has the following pcrcentage composition:

Sodium cyanide 35.09 Sodium carbonate 30.25 Sodium chloride 21.90 Calcium carbonate .14 Combined -water (water of crystallization) 6.08

The articles to be treated, having been preheated in the furnace 2 to approximately the temperature of the fused bath in the pots 10, are depositedv by means of the transfer arms 4 in the pot 10 which, at the moment, is opposite to the transfer device. The circular framework carrying the pots 10 then moves to bring the next pot into position to receive a. charge of preheated articles.A

rllhe loading of the articles may take plate .at intervals of about live minutes, and the treated articles are removed from the pots 10 when they come into the position next to the charging position,` in which case each article remains i'n the cyanide bath for about a half hour, assuming the seven of the pots 10 are employed as shown in the drawing. A longer treatment in the cyanide bath is sometimes desirable, and this may be secured by moving the framewhich carries the treating pots at intervals of ten minutes, for example, instead of at intervals of five minutes, or by providing a larger apparatus with a correspondingly larger number of treating pots. When the apparatus having seven vboxes is moved at ten-minute intervals the furnace 2 may still operate to deliver articles at five minute intervals, two charges being placed in each of the pots 10.

After being removed from the cyanide bath thearticles are ouenched in oil or water, according to the usual case-hardening practice.

` rllhe preliminary heat treatment is employed for the 'purpose of completely removing any external strains that mayl have been set up in the articles during their manufacture, and thus rendering the metal capable of uniformly receiving the hardening matelos rial.. This preheating should be sufficient content of the steel before reachin V thusreducing its ultimate strength below.

' preferably process described above, and leaving thel chains in the fused bath for about 1 hour and 5 minutes, the chains are found to have a clear and uniform penetration of carbonl to about 31E of an inch, the carbon content then varying toward the center of the metal and being reduced to the original carbon the center. `The depth of penetration of t e carbon varies according to the time of treatment in the fused bath. This time should not be less than 30 -or 45 minutes when treating cross-chains for vehicle wheels.

In the articles treated in this manner the structure of the metal at the center is not changed in any way, and the distribution of the carbon in the outer layers is remarkably uniform. In the ordinary pack-hardening systems the carbon enters the metal irregularly and may penetrate to the center of the article at one side, while stopping far short of the center on another si Also, the ordinary case-hardening processes tend to weaken the central core of the article,

the strength of the original metal. The articles produced accordin to m process, on the contrary, are entire y uni orm both as to the depthof penetration of the carbon and as to the nature of the hard layer produced on the surface, and are wholly 'unchanged as to the composition and strength of the central core. Also, the several articles of a given kind, such as chain links are uniform with each other as to the depth of penetration of carbon and the nature of the surface layer. I attribute these results to the preliminary heating of the metal which gives it a uniform structure reassembling the structure of annealed metal, and to the time of treatment -which enables the carbon to penetrate evenly. For the best results, the temperature to which the metal is heated, and the temperature of the vfused bath,

-should be as high as practicable, butnot above the point where the metal is harmed by excessive heat treatment. I have found `that this up er limit of temperature is inv the neighbor ood of 1800 F. v

The preheated articles are slightly cooled while being transferred from the furnace to the treating pots, and therefore they are rought to a temperature correvspondingly above the temperature of the immersing fused bath, so that they enter the vbath at approximately the same temperature as the fused material.

The details of structure, materials and manipulation described above are not to be understood asvlimiting my invention, which may be applied in various ways, within the scope of the appended claims.

I claim as my invention y 1. The process of hardening iron andi steel that comprises reheating the metal to be hardened to atA east its upper critical point and then immersing the preheated.

metal in afused bath containing a cyanide.

2. The process of hardening .inon and f2' steel that comprises preheatingthe metal to be hardened to at least its upper critical point and then immersing the preheated metal in a fused bath containing a cyanide,

the temperature of the metal bein at least as high as the temperature of t e fused bath.

3. The' process of hardening iron and) steel that comprises preheating the metal to be hardened to at least its upper critical point and immediately immersing the heated metal in a fused cyanide-containing bath of approximately .the same temperature as the metal. Y

4. The process of hardening iron and steel that comprises preparing a fused bath containing a cyanide, heating the metal to be hardened to at least the same temperature as the bath, immersing the ,said metal in the said bath fora perlod of at least thirty minutes, and quenchi the said metal.

5. The process ofnardening iron and steel thatcomprises preparing a fused bath containing a cyanide and, in addition, at least one alkali-netalSalt, heating the metal to be hardened to at least the same temperature as the bath, immersing the said metal in the said bath for a period of at least thirty minutes, and quenching the said metal.

hardened to at least the same 'temperature as the bath,- immersing the said metal in the said bath vfor a period of at least thirty minutes, and quenching the said metal.

7. The process of hardening iron and.'

steel that comprises preparing a fused bath containing a cyanide, heating the said bath to-a temperature between 1200 F. and 1800 F., heatlng the metal to be hardened to at least the same temperature as the said bath, the said metal in the said bath for a period of at least thirty minutes, and quenching the said metal.

8. The process of hardening iron .and steel that comprises preparing a fused bath containing a cyanide, heating the said bath to at least 1650 F., heating the' mete?. to

he hardened to at least the same temperature es the bath, immersing the seid metal in the said bath for a period of et leest thirty O minutes, and quenching the seid metal.

9. The process of hardening iron and steel that comprises preparing a fused hath containing a. cyanide, sodium chloride end sodium carbonate, heating the seid beth, to

io et leest 1650" 1F., heating the metal to he hardened to at least the seme temperature sibeeegeeii es the hath, ieirsng the seid metal in. the'- seid-heth fon @period of et leest thicty minutes, end then quenching the seidnuetel in e cooling beth. 15

iin testimony whereof, ii the' seid FRANK A. BOND have' hereunto set my hand.

FRANK A. BND. rWitnesses z R. W. Beown, JOHN F. 

